Animal collars having insecticidal activity are known and are commercially available. They protect small animals, in particular dogs and cats, against infestation by Mallophaga and Siphonaptera and, in some cases, also against Ixodidae.
In general, the carriers for the collars hitherto commercially available are prepared by extruding polyvinyl chloride thermoplastics. Other natural and synthetic resins and thermoplastics have also been described as carriers for insecticides (see, for example, French Pat. No. 1,568,198), usually having O,O-dimethyldichlorovinyl phosphate (DDVP) as the insecticidal component. However, collars based on DDVP have some disadvantages, such as, for example, the occasional occurrence of skin irritation. Additionally, the collars suffer from a short life due to the high volatility of DDVP.
U.S. Pat. No. 3,852,416 describes animal collars based on polyvinyl chloride, using less highly volatile carbamates as insecticidal active compounds. Compared with these collars, animal collars according to the present invention are distinguished by an increased activity and a longer period of action.
In the following text, the vapor pressures of different ectoparasiticides are compared with one another. The vapor pressure at 20.degree. C. is given in each case.
DDVP: 1.2.times.10.sup.-2 mm Hg PA0 Propoxur: 6.5.times.10.sup.-6 mm Hg PA0 Diazinon: 8.4.times.10.sup.-5 mm Hg PA0 Dimethoate: 8.5.times.10.sup.-6 mm Hg
In the case of highly volatile substances such as DDVP, the active compound passes from the collar directly into the gas phase. In the case of the less volatile substances, such as, for example, Propoxur, the active compound sublimes out of the collar and forms a white dust on the surface of the collar. Some of this passes into the vapor phase and is active there and some is distributed in the form of the dust over the animal to be treated.
Sublimation (or "efflorescence" or "exudation") of the active compound onto the collar surface has the following disadvantages:
(1) On prolonged storage, more active compound sublimes onto the surface and becomes concentrated there. When the collar is used, there is a very high dose of active compound on the surface, which ensures good immediate action but may thereby approach the point of being slightly toxic.
(2) The active compound present on the surface is rubbed off while the compound within the collar comes to the surface very slowly. Thus the release of the active compound is not linear over as long as possible a period as is desired.
(3) The crystallizing out of the active compound on the surface of the plastic coller makes the latter look extremely unattractive giving the appearance of being dusty or moldy.